The present application claims priority under 35 U.S.C. xc2xa7119 to Japanese Patent Application No. 2001-170269, filed on Apr. 30, 2001, the entire contents thereof are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to crankshaft support structure of an engine.
2. Description of Background Art
A crankshaft which is supported by a main bearing and to which a sprocket is fitted is disclosed in Japanese patent No. 2813011. FIG. 3 shows one example of such crankshaft support structure, and highlights crankshaft 1, main bearing 2, inner race 3, ball 4, outer race 5, crankcase 6, timing sprocket 7 fitted onto the periphery of the crankshaft 1, and timing chain 8. The outer diameter R1 of the timing sprocket 7 is set so that it is smaller than the inner diameter R2 of the inner race 3. The crankshaft 1 is fitted with timing sprocket 7 beforehand. During assembly, the crankshaft is passed through the inside of the main bearing 2, the main bearing having previously been fixed to the side of the crankcase 6.
With this conventional structure, since the crankshaft 1 integrated with the timing sprocket 7 must pass inside of the main bearing 2 during assembly, the inner diameter R2 of the inner race 3 of the main bearing 2 must be larger than the outer diameter R1 of the timing sprocket 7. As a result, the size of the main bearing 2 is regulated by the timing sprocket 7. This limits the ability to miniaturize the main bearing 2. As a result, the main bearing is larger and heavier than is desireable.
The object of the present invention is to develop a smaller and lighter crankshaft support structure.
To accomplish this objective, engine crankshaft support structure according to the invention is based upon an engine in which a sprocket for driving a timing chain for driving a camshaft is arranged outside a main bearing for supporting a crankshaft. The structure includes an outer race of the main bearing which is press-fitted and fixed to a crankcase, an inner race of the main bearing is separated from the outer race and is loosely fitted onto the periphery of a crankshaft, and the sprocket for driving the timing chain which is press-fitted onto the periphery of the crankshaft for holding the inner race of the main bearing in place.
An oil seal mounting flange is integrated with the sprocket for driving the timing chain, and a side part of the flange presses against the inner race of the main bearing.
According to the invention, as the outer race of the main bearing is press-fitted and fixed to the crankcase, the inner race is separated from the outer race and is loosely fitted to the crankshaft and the inner race is fixed by press-fitting and fixing the timing sprocket to the crankshaft. Further, the crankshaft which has been integrated with the inner race beforehand is made to pass inside of the outer race of the main bearing, the main bearing having been previously press-fitted and fixed to the crankcase. Thus, the inner race is fitted inside of the outer race, and the main bearing is formed.
As a result, the inner diameter of an inner bearing can be made smaller than the outer diameter of the timing sprocket, and the size of the main bearing can be minimized. Therefore, the main bearing can be made smaller and lighter than previously possible. Also, oil seal mounting structure can be simplified by using a flange for mounting both an oil seal and the timing sprocket, as well as for pressing against the inner race to hold it into place.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.